For the rapid progress of high technology, especially the mighty changes in the field of micro electrical technology, the electrical related products have been deep embedded in every family and business, becoming the necessary part of the modern life.
Certainly, the more demands of human being, the more functions of electrical elements and the smaller size thereof is required. However, these delicate electrical elements need more concentrated devices to reduce the occupied space, and the problems such as transmission line impedance, the distance between two lines, and the layout rules need to be considered thus causing the circuit layout become more and more difficult.
Please refer to FIG. 1, showing the profile of multi-layer substrate structure in the prior art. The multi-layer substrate 1 includes a first core circuit board 11, a second core circuit board 12, and a differential signal process layer 13 located between the first core circuit board 11 and the second core circuit board 12. On the other side of the first core circuit board 11 is a power supply layer 14, and on the other side of the second core circuit board 12 is a grounding layer 15 corresponding to the power supply layer 14. In general, the differential signal process layer 13 can transmit the non-inverted and inverted data that are totally the same and signed as + and − respectively in the figure through two traces from a differential signal transmitter (not shown in the figure) and finally received by a differential signal receiver (not shown in the figure). Because of the type of differential signal, voltage swing can be largely reduced thus increasing the speed in the circuit and further reducing the amount of power consumption and the effect of Electro-Magnetic-Interference (EMI). Besides, on the power supply layer 14 is a single transmission line layer 16, which is isolated from the power supply layer 14 with a dielectric layer 17 to enable the single transmission line layer 16 to transmit signals. In addition, a third core circuit board 18 is formed on the single transmission line layer 16, and a second grounding layer 19 is formed on the third core circuit board 18. The first grounding layer 15 and the second grounding layer 19 respectively have a circuit layer 21 formed on the other side of the corresponding grounding layers. Moreover, to obtain the effect of anti-solder and to protect the circuits on the circuit layer 21 from any scratches causing short circuit or open circuit, a protection film 22, called Solder mask, are formed on the circuit layer 21.
However, the differential signal process layer 13 of the said multi-layer substrate 1 is a kind of plane structure and must be formed in a pair, so along with the rising of designing complexity and difficulty, incomplete signal transmitting problems such as noise coupling and signal distortion will be occurred in such plane circuit board because of the insufficient board surface area, causing poor layout. Thus how to resolve the aforesaid problems to reduce cost and promote production competitiveness has been of great urgency.